The present invention relates to a method of manufacturing a semiconductor integrated circuit device, an optical mask therefor, its manufacturing method, and mask blanks; and, more particularly, the invention relates to a technique which can be effectively applied to the exposure technique used in the process of manufacturing a semiconductor integrated circuit device.
In the manufacture of a semiconductor integrated circuit device, a lithography technique is used as a method of transferring micro patterns onto semiconductor wafers. In the lithography technique, a projection exposure system is mainly used; wherein, the pattern of a photo mask provided on the projection aligner is transferred onto a semiconductor wafer to thereby form a device pattern.
The ordinary photo mask examined by the present inventor is made by processing a light screening material such as chrominum (Cr) or the like formed on a transparent quartz substrate. In other words, the photo mask is constituted in such a manner that a light screening film comprised of chromium or the like is formed in a desired shape on the quartz substrate. The processing of the light screening film is carried out, for example, in the following manner. After an electron-beam-sensitive resist is applied onto the light screening film, a desired pattern is written on the electron-beam-sensitive resist by an electron beam lithography system. Subsequently, after the resistor pattern of a desired shape is formed by development the light screening film is processed by dry etching or wet etching by the use of the thus obtained resist pattern as a mask. After this, the resist is removed, cleaning or the like is carried out, and thus, a light shielding pattern of a desired shape is formed on the transparent quartz substrate.
Further, recently, various mask structures have been proposed for the purpose of enhancing the resolution of the lithography. For example, in Japanese Patent Laid-Open No. 136854/1992, there is disclosed a mask structure constituted in such a manner that, as a means for enhancing the resolution of a single transparent pattern, the portion surrounding the single transparent pattern is made semitransparent, in other words, the light screening portion of the photo mask is made semitransparent; and, thus, the phase of the slight amount of light passing through this semitransparent portion and the phase of the light passing through the transparent pattern are inverted with respect to each other. In other words, light that is below the sensitivity of the photo resist for transferring the pattern is allowed to pass through the semitransparent film, and the phase of this light and the phase of the light which has passed through the transparent pattern are inverted with respect to each other. The light which has passed through the semitransparent film is inverted in phase with respect to the light which has passed through the transparent pattern, which is the major pattern, so that its phase is inverted in the boundary portion of the patterns, and thus, the light intensity in the boundary portion approaches 0. As a result, the ratio between the intensity of the light which has passed the transparent pattern and the intensity of the light in the pattern boundary portion becomes large; and thus, a light intensity distribution with a contrast higher than in the case of the techniques using no semitransparent film is obtained. This is called a halftone type phase shift mask. In the manufacturing process of the halftone type phase shift mask, the light screening film of the above-mentioned ordinary photo mask is altered to a halftone phase shift film, so that the halftone type phase shift mask is manufactured by approximately the same process as the above-mentioned ordinary photo mask manufacturing process.
Further, for example in Japanese Patent Laid-Open No. 289307/1993, there is disclosed a method of forming a light screening film by the use of a resist film for the purpose of simplifying the photo mask manufacturing process and enhancing the precision. This method utilizes the properties of an ordinary electron-beam-sensitive or an ordinary light-sensitive resist that screens the vacuum ultraviolet rays with a wavelength below about 200 nm. According to this method, the step of etching the light screening film and the step of removing the resist are disused; and thus, the reduction in cost of the photo masks, the enhancement in dimensional accuracy thereof, and the reduction of defects thereof become possible.
Further, in Japanese Patent Laid-Open No. 181257/1993 for example, there is disclosed a so-called halftone mask constituted in such a manner that, on a substrate which is transparent with respect to the exposure light, a phase shift film comprising a semitransparent material which absorbs the exposure light is provided. In case of the technique disclosed in this Japanese Patent Laid-Open No. 181257/1993, the mask vacuum-holding surface is the mask substrate surface, so that exposure is executed with the mask surface directed to the exposure light source. In this case, the mechanical strength of the phase shift film comprising a semi-transparent material is high even at the periphery of the mask, and there is no problem with respect to mask absorption and the like. Further, as for the mask alignment, the mask has light screening properties, and thus, there seems to be no problem.
Further, in Japanese Patent Laid-Open No. 15830/1997 for example, there is disclosed a technique according to which, after a light shielding pattern is formed on a mask substrate, a phase shift film is formed to a film thickness greater than the film thickness corresponding to the target phase difference, and a desired portion provided with the phase difference is etched by an amount corresponding to the target phase difference.
However, in case of the above-mentioned technique, according to which the light shielding pattern on the photo mask is formed by a resist film, there are not disclosed the problematic point encountered when the photo mask is actually used in the process of manufacturing a semiconductor integrated device, the problematic point encountered in the actual photo mask manufacture, and the measures to counter these problematic points; and, the present inventor has found that the above-mentioned technique has the following problems.
More specifically, it is difficult to detect predetermined patterns, such as, e.g., an alignment mark, a pattern measuring mark or a product decision mark on the photo mask, which are used for the detection of various kinds of information. For example, in the case of a photo mask defect inspection system, an aligner and the like, which are used at present, a halogen lamp or the like is mainly used for the alignment of the photo mask. Accordingly, in case the photo mask is mounted on a defect inspection system or an aligner, if the detection mark on the photo mask is formed by a resist film pattern, then no high contrast can be obtained, since the resist mask is high in light transmissivity; and thus, the detection of the pattern is difficult. Due to this, it becomes difficult to align the photo mask with the defect inspection system or the aligner, and thus, there arises the problem that no good inspection or exposure can be made.
Further, when the photo mask is mounted onto the defect inspection system or the aligner, foreign matter is produced. In the case of the above-mentioned technique, when the photo mask is mounted onto the defect inspection system or the aligner, the resist film of the photo mask comes into direct contact with a photo mask fixing member (such as, e.g., a vacuum fixing member) of the defect inspection system or the aligner, so that, upon the breakage or peeling-off of the resist film, foreign matter is produced. This foreign matter tends to attach to the surface of, for example, the lens of the inspection system or the aligner, to contaminate the inside of the chamber or to attach to the surface of the semiconductor wafer, as a result of which, a deterioration of the inspection accuracy or the transfer accuracy of the pattern is brought about, and defects, such as short-circuit or open-circuit defects of the pattern are caused. Thus, the reliability and manufacturing yield of the semiconductor integrated circuit devices fall, this being another problem.